The present invention relates to a system for providing short circuit protection to an electrical circuit that connects a device to a DC power source. In particular, the present invention is considered suitable for removing voltage from the circuit that connects a vehicle starter to a battery during the periods when current is not needed to power the starter.
Motor vehicles, such as cars, marine vessels, trucks and the like almost universally include a battery that is used for engine ignition. The battery is electrically connected to a starter that is used to crank the ignition. Typically, the starter is actuated by a solenoid relay located adjacent the starter. As a result, the conductor that carries current from the battery to the starter solenoid contains the voltage supplied by the battery. In addition, the conductor is typically sized to carry a significant amount of current needed to drive the starter.
In a typical motor vehicle 12 volt electrical system, the current that goes through the starter circuit has an initial surge of 900 to 1500 amps and has a steady state current of 200 to 600 amps for about six seconds. Of all the electrical cables in a motor vehicle, the starter cable can provide the most energy at a short. It is impractical to protect the starter circuit with a fuse since a large fuse would be required to support the current needed to power the starter. This size fuse would provide little or no protection during the periods of time when current is not needed to operate the starter. As a result, in certain conditions, such as when the starter circuit wire insulation is cut or pierced, an unprotected starter circuit could cause electrical arcing or short circuits. This could shut down the vehicle or damage other components.
Some existing battery protection devices are capable of shutting off power to the entire electrical system under certain conditions. Such conditions include detection of a short circuit condition, battery low voltage, or activation of a theft deterrent system. Likewise, short circuit current sensors can be used in a system to shut off current after a short condition occurs. However, these devices shut off current only after the short has already occurred.
As the need for energy in motor vehicles increases with the introduction of more electrically powered components and systems, vehicle manufacturers are contemplating the introduction of higher voltage electrical architectures. Current proposals contemplate replacing 12 volt systems with a 42 volt system. The use of higher voltages increases the probability that a damaged starter cable could result in an electrical arc. The use of higher voltages also increases the amount of energy available to damage vehicle components and systems. Therefore, higher voltage vehicle electrical systems will need short circuit protection.
Thus far, the prior art does not adequately address prevention of short circuits and electrical arcing in a starter circuit.
The present invention overcomes the problems noted above and satisfies a need for a short circuit protection system for an electrical circuit that connects a battery to an unfused device. The invention overcomes the problems of the prior art by providing a system that removes voltage from the circuit that electrically connects a device to a DC power source, such as a battery, during periods when the device does not require power.
The present invention is particularly useful to protect a starter circuit from short circuits, electrical arcing, and current leakage. In contrast to battery disconnect systems known in the prior art, this invention can remove energy from a single circuit without shutting down power to the entire electrical system. The present invention can thus be incorporated with battery protection systems and anti-theft systems known in the prior art. When used as a motor vehicle starter circuit protection system, the present invention protects the circuit while the vehicle is in operation. Other vehicle battery disconnect systems disconnect power only when conditions such as low battery voltage are detected.
In accordance with the present invention, a short circuit protection system is provided to electrically protect a section of conductor that is a part of the conductive path between a DC power source, such as a battery, and a device powered by the DC power source. The system comprises two switches in the conductive path between the battery and the device. It also includes a microprocessor capable of receiving inputs indicating that the device is to be turned on and shut off and further capable of generating outputs to open and close the two switches.
In accordance with the present invention, a method is provided to remove voltage from a section of electrical conductor that is a part of the conductive path between a DC power source, such as a battery, and a device powered by the DC power source. A preferred method comprises the steps of detecting a signal indicating the device is to be shut off, opening a switch that lies in the conductive path between the device and a first end of the section of conductor to be protected, and then opening a second switch that lies in the conductive path between the battery and the other end of the section of conductor to be protected. An advantage of using this method is that the switch located between the battery and the section of conductor to be protected closes when there is no electrical load. As a result, this switch can be designed to be less rigorous than the switch located between the device and the section of conductor to be protected.
In accordance with another preferred aspect of the present invention, the method includes the steps of detecting a signal indicating the device is to be turned on, closing the switch that lies in the conductive path between the battery and a first end of the section of conductor to be protected, and then closing a second switch that lies in the conductive path between the device and the second end of the section of conductor to be protected. Once these steps are completed, power is provided to the device. The method further comprises the steps of detecting a signal indicating the device is to be shut off, opening the second switch that lies in the conductive path between the device and second end of the section of conductor to be protected, and then opening the switch that lies in the conductive path between the battery and the first end of the section of conductor to be protected. As a result, power is first removed from the device then removed from the section of conductor to be protected. An advantage of using this method is that the switch located between the battery and the first end of the section of conductor to be protected always closes and opens when there is no electrical load. As a result, this switch can be designed to be less rigorous than the switch located between the device and the section of conductor to be protected.
It is thus an object of the present invention to provide an improved system that removes voltage from a section of the circuit that electrically connects a battery to a device powered by the battery;
It is yet another object of the present invention to enable the use of a switch in the conductive path that is less rigorous than a second switch located in the conductive path.